1. Field of the Invention
The present invention relates to a method for manufacturing agglomerates of sintered pellets, and more particularly to a method for controlling operations in manufacture of agglomerates of sintered pellets by the use of sensors.
2. Description of the Prior Arts
Fine iron ore, flux such as serpentine and return fines are blended and mixed by a mixer, and a mixture thereof is pelletized by a primary pelletizer. Pelletized materials made by the primary pelletizer are coated with a solid fuel and green pellets of 5 to 10 mm in particle size are manufactured. Said green pellets are charged into a grate type sintering machine and sintered. Sintered pellets are crushed into particles of predetermined size. Then, they are cooled and classified whereby agglomerates of 4 mm or more in size are manufactured.
The following control is carried out during manufacture of agglomerates of sintered pellets.
(a) A worsening of permeability of green pellets charged into a sintering machine is found through a fall of temperatures of a plurality of wind boxes on a discharge side of agglomerates and a rise of suction pressure of a main blower. Moreover, positions of a burn through point are controlled. The positions of the burn through point are determined by measuring wind box temperatures of the sintering machine and finding positions of the wind boxes having the highest temperature from a distribution of the wind box temperatures. A pallet speed is controlled so that the positions of the burn through point can be optimum positions.
(b) A difference in the wind box temperatures in a direction of a width of the wind box or a difference in a high temperature zone of an agglomerate discharge portion in a direction of a width of the layers are estimated. Densities of charged green pellets in a direction of a width of the sintering machine are controlled to make uniform a sintering speed in a direction of the width of the sintering machine on the basis of estimated differences in the direction of said widths.
In the above-mentioned method (a), the worsening of permeability of the pellets can be found only 30 to 35 minutes later after pellets of bad permeability charged into the sintering machine have passed an ignition furnace. Moreover, the reason for the worsening of the permeability is not understood if it is caused by a bursting of the green pellets or the other reasons. Since it takes much time to understand the reason for the worsening of the permeability, there occur a decrease of a productivity and lowering of quality of products.
In the case of using the difference in the wind box temperatures in the above-mentioned (b), there occur errors due to an air leakage. Therefore, only when a portion where the sintering speed is ununiform reaches the wind box on the side of the agglomerate discharge portion, the difference in the wind box temperatures in the direction of the width thereof can be detected. The difference in the high temperature zone in the direction of the width thereof can be detected only when a portion of abnormal sintering reaches the agglomerate discharge portion. That is, only 30 to 40 minutes later after the charge of the green pellets into the sintering machine, occurrence of the portion of abnormal sintering can be detected. Due to delay of a detection of the abnormal sintering, a control of the densities of the charged pellets in the direction of the width of the sintering machine delays. Accordingly, there are problems such that the productivity and the yield of agglomerates of sintered pellets lower.